The production of lumber involves the application of a stamp on a planed board that will remain with the board until it reaches the end user. These stamps primarily show the grade and sometimes other attributes of each piece of lumber. There are various sanctioning organizations that insure the quality and integrity of the various grades of lumber produced. These sanctioning organization control the issuing of stamps and their use. In addition to grade identification, stamps can be used to identify moisture content and heat treatment (for pest pasteurization) which is generally required on exported products.
For example, with southern yellow pine (SYP), most of the stamps are controlled or governed by SPIB http:www.spib.org/, which is an organization that sets and inspects the rules for each lumber grade. The stamp typically includes the grade mark, which identifies the grade of the board, and an identification indicating the SPIB “member” that manufactured the lumber. Generally, the board is only stamped in one location. However, recent market changes have required additional stamp locations along the lengthwise face of the board.
HT (heat treated for pest pasteurization) stamps usually are required to be applied to any wood packaging materials of any length being exported. Many manufacturers export two foot blocks that have been trimmed from the longer lengths of lumber to remove defects. Each two foot block must be marked with the HT stamp. The HT stamp cannot have a grade. The HT must state KD 19 HT. The U.S. Department of Agriculture Animal & Plant Health Inspection Service (APHIS) has entered into a Memorandum of Understanding with the Southern Pine Inspection Bureau (SPIB). The overall direction and control of the cooperative program is to be maintained by APHIS. The program provides the necessary documentation that kiln dried southern pine lumber exported to foreign countries has reached a critical temperature at the core to eradicate the “Pinewood Nematode” and its vectors (56° C./133° F. for 30 minutes). The HT mark is not limited to yellow pine, and is also used for other lumber types.
Mechanical printers, generally known as “grade printers,” have been widely used in planer mill applications many years, stamping the grade on each individual piece of lumber using rubber stamps. The rubber stamps are typically located on rotating wheels with only one stamp being located on each wheel. The appropriate arm is lowered with a cylinder when the corresponding piece of lumber transverses beneath the rotating wheel. The wheel must travel the same lineal speed as the lumber to avoid smearing the stamp on the lumber. Presently, the wheels are driven by roller chains from the head shaft of the lugged conveyor that the boards are traversing on, i.e. the wheels are mechanically timed with the conveyor by the chains.
The lumber is generally transported on lugs, with one board per lug, transversely through a mill. Grade printers are located downstream of a board trimmer to apply a stamp to each board. For example, a lumber grader might call for grade #2-8′ on a near end of a board and grade #3-10′ on a far end of the board. When this happens, the trimmer will cut an eighteen foot board in two pieces at approximately an eight foot position. As these two pieces come out of the trimmer, the far end piece will be picked up and “jumped” into the empty lug behind it. Once these different grade boards are on different lugs, they can be stamped with the appropriate gradestamps.
In addition, the stamps must also be timed to land, preferably centered, on the width of the board. Thus, for different width boards, such as 4, 6, 8, 10 and 12 inch boards, the stamp might not be located in the same position on a 4 inch wide board as on a 12 inch wide board. The timing is generally done mechanically, either with adjustable sprocket assemblies or an on-the-fly mechanical adjustment requiring a series of sprockets in a cross-shaped pattern.
Many mills desire to stock longer package lengths, such as 16, 18 and 20 foot lengths, with the ability to cut the finished package into two shorter lengths. If this is done, each end of the board must contain the same grade stamp so that when they are cut in two smaller sections, each piece will include the required grade stamp. When stamps, including the grade are required on each end of the board, the conventional grade printer must span across the conveyor and similar grade stamping arms must be placed on the far end of the board.
HT stamps must be placed every two feet or less on the board upstream of the trimmer to mark two foot cut-offs prior to trimming. Thus, when the stamp must include HT, two printers are required, the HT printer upstream of the trimmer and the grade printer downstream of the trimmer. Since the two foot blocks are normally dropped out to a turntable to be hand stacked, the HT stamp can be applied in the block conveyor or manually by the turntable operator.
The printers are mechanically driven via roller chain drives from the main drive. Chain slack and surge cause numerous maintenance problems and increase costs. There is generally insufficient room on present printers to include 6-8 grades on each end of a board and HT marks on 2 foot centers without interfering with the lugged chains that transport the lumber on 2 foot centers.
In view of the many shortcomings of present lumber printers, there is a great need for a printer that is capable of cost effectively applying stamps having different grades and other information, such as HT, manufacturer and dryness to lumber in one efficient step.